Considerable research has been undertaken to determine the mechanics and chemistry of surface corrosion on the water-side of metal equipment in an effort to improve the life of such equipment. Most of the research has centered around the passivation of the surface by treating the water or adding to the service water or as a pretreatment of the metal surfaces prior to contact with the service water, agents found to passivate and/or reduce the redox reactions which occur due to the presence of dissolved gases such as oxygen, carbon dioxide and hydrogen resulting from leaks, as well as, degradation of the water from couple reactions between different metals in the system and the thermal patterns of these metals in service. It has become common practice to remove scale and corrosion product deposits to restore the tubing to near its original diameter and improve surface film flow characteristics. It is also common practice to passivate the metal surfaces including metal deposits which may form during such cleaning procedures, since these deposits can create electrical couples throughout the system dissolving away metal and thus reducing the structural integrity of the tube and/or piping.
It has become standard practice to clean the water-side surface of metal equipment, such as heat exchanger tubes, boiler tubes and the like, by treating the water-side surface with an acid, usually an aqueous acid such as hydrochloric acid, to remove the scale which is deposited from the water and/or results from reaction of the metal surface with the water and/or oxygen during the in-service period of the equipment. This acid treatment is followed by at least one and conventionally two aqueous treatments; one, optional, to flush the acid from the equipment, and the other, to neutralize any residual acid remaining on the surface. Conventionally, this type of cleaning is carried out by providing the treating agents or fluids in the form of a foam, although other techniques may be used, as for example, hydraulic pressure cycles or the like.
It has now been found that present day advanced techniques for cleaning copper alloy metal surfaces leaves the surface lightly fouled with copper precipitates which, if not removed, in time cause corrosion through the bi-metal couple, as well as, creating an environmentally undesirable waste problem during start-up of a just cleaned unit due to the presence of copper in the effluent discharge during the water chemistry passivation of the surfaces when the equipment is placed back in service.
It would therefore be advantageous to the industry if an additive and/or additives could be found which would reduce the presence of copper deposits normally found in acid cleaning of copper alloy surfaces, and, thus reduce, if not eliminate, the presence of copper redeposited and copper in any form in effluent waters from the system. These and other objects will become apparent to those skilled in the art from the following description and examples.